1. Field of the Invention
This invention relates to catalysis, and particularly to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organosulfur, organonitrogen, organometallic and asphaltene compounds. More particularly, this invention relates to a hydroprocessing catalyst and a process for utilizing the catalyst for hydrodesulfurizing, hydrodemetallizing and converting asphaltene compounds in hydrocarbon liquids.
2. Description of the Prior Art
In a typical catalytic hydrocarbon refining process, contaminant metals and coke from a hydrocarbon oil deposit on porous refining catalysts, causing a gradual loss of catalytic activity and/or selectivity for yielding an intended product. Residual petroleum oil fractions, such as the heavy fractions produced in atmospheric and vacuum crude distillation columns, are especially undesirable as feedstocks for most catalytic refining processes due to their high metals, asphaltene and sulfur content. Economic considerations, however, have recently provided new incentives for catalytically converting the heavy fractions to more marketable products.
Methods are available to reduce the sulfur, metals and asphaltene content of residua. One such method is hydrodesulfurization, a process wherein a residuum, usually containing the bulk of the asphaltene components of the original crude from which the residuum was derived, is contacted with a catalyst usually containing hydrogenation metals on a porous support material under conditions of elevated temperature and pressure and in the presence of hydrogen such that the sulfur components are converted to hydrogen sulfide, and the asphaltene components to lower molecular weight molecules while coke and metals are simultaneously deposited on the catalyst. However, the deposition of coke and contaminant metals on the catalyst causes deactivation of the catalyst, and, in the usual instance, the extent of deactivation is a function of the amount of coke and/or metals deposition on the catalyst surface, i.e., the usefulness of the catalyst steadily decreases as the amount of deposited coke and/or metals increases with continued treatment of the residuum.
It has been recognized that typical hydroprocessing catalysts, especially those utilized for hydrodesulfurization purposes, have specific pore size characteristics effective for catalytic processing of residuum. For example, a catalyst employed in a two-catalyst hydrodesulfurization process ordinarily includes at least one desulfurization catalyst having a sizable number of pores of diameter less than 100 angstroms. Although such a catalyst often exhibits high desulfurization activity, its useful life is manifestly short in the absence of a catalyst promoting metals removal. Conversely, many catalysts exhibiting a suitable degree of demetallation activity tend to have a sizable number of pores having a diameter greater than 300 angstroms. The hydrodesulfurization processes disclosed in U.S. Pat. Nos. 3,819,509 and 3,901,792 are typical of those employing a catalyst having relatively small pore characteristics (i.e., some pore diameters less than 100 angstroms) for desulfurization and a second relatively large pore catalyst additionally promoting metals removal.
Although conventional catalysts, including those containing both large pores (i.e., greater than 300 angstroms pore diameters) and small pores (i.e., less than 100 angstroms pore diameters) are somewhat active and stable for hydrocarbon conversion reactions, catalysts of yet higher activities and stabilities are still being sought. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of a catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur, asphaltene, and/or contaminant metals content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended due to such factors as lower coke formation or the deposition of less metals.
Presently, conventional catalysts employed to promote hydrodesulfurization of a hydrocarbon oil tend to have limited capability for also converting asphaltenes to less complex components. Although such conventional catalysts may be active for removing sulfur, the useful life of such catalysts may be relatively short when high demetallization activity and/or asphaltene conversion is also emphasized.
A need still exists for a process employing a highly active hydroprocessing catalyst with an extended useful life to promote hydrocarbon conversion reactions, particularly hydrodesulfurization, hydrodemetallization and/or hydroconversion of asphaltenes.
Accordingly, it is an object of the present invention to provide a catalytic hydrocarbon conversion process that promotes the upgrading of a hydrocarbon oil, particularly with respect to converting asphaltenes to lower molecular weight molecules in addition to removal of sulfur compounds.
It is another object to provide a process for hydrodesulfurizing a hydrocarbon oil while maintaining a high degree of asphaltene conversion.
It is still another object of the invention to provide a process employing a catalyst for hydroconverting asphaltenes in a hydrocarbon oil and, specifically, to provide a hydrocarbon conversion process employing a catalyst with high activity and stability for converting asphaltenes to materials that can be subsequently more effectively converted to lower molecular weight product hydrocarbons.
It is a further object of the invention to provide novel processes for the hydrodemetallization, hydrodesulfurization and hydroconversion of asphaltenes found in heavy hydrocarbon oil fractions such as residua.
It is an object of the invention to provide a multi-stage hydrocarbon conversion process, and more particularly, to provide for the hydrodesulfurization of a residuum hydrocarbon oil by contacting the oil with a demetallization catalyst, followed by contact with a catalyst having high activity and a long useful life with respect to asphaltene conversion in addition to sulfur removal, and then contacted with a cracking catalyst.
These and other objects and advantages of the invention will become apparent from the following description.